In the fabrication of semiconductor-based devices (e.g. integrated circuits or flat panel displays), layers of material are alternately deposited onto and etched from a substrate surface (e.g., the semiconductor wafer or the glass panel). As is well known in the art, the deposition of material layer(s) and etching of the material layer(s) may be accomplished by a variety of techniques, including plasma-enhanced deposition and etching. In plasma-enhanced deposition or etching, the actual deposition or etching of the substrate takes place inside a plasma processing chamber. During the deposition or etching process, a plasma is formed from a suitable source gas to deposit a material layer on the substrate or to etch areas of substrate that are unprotected by the etch mask, leaving behind the desired pattern.
Silicide films are used to provide low resistance interconnection paths which are important in order to fabricate dense, high performance devices. One structure is a polycide gate of the MOS transistor. It consists of a refractory metal silicide (e.g., WS2, TiSi2, MoSi2, or TaSi2) on top of a doped poly-silicon layer. In an example process, such a structure reduces the interconnect resistivity to less than the 15-30 ohms/square exhibited by doped poly-silicon that has no silicide. As minimum geometries decrease, interconnect resistances increase. For technologies with minimum geometries of about half a micron, introducing a refractory metal polycide process significantly lowers gate interconnect resistance. In minimum geometry features, tungsten silicide is the material of choice for its low sheet resistances and thermal stability.
The current existing tungsten silicide etching process has a severe etch rate micro-loading problem. Tungsten silicide in an isolated feature area is etched at a higher rate than in the dense feature area. Due to the severe degree of micro-loading, longer over-etch operations are required at the expense of increasing the risk of gate oxide punch through, which reduces device yield.
In view of the foregoing, there is a need for a method that provides an improved tungsten silicide etching process with a reduced etch rate micro-loading effect.